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![]() Intel and compatable CPU's Programming Information ![]() |
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Intel SSE MMX2 KNI documentation AMD 64 Bit & Opteron resource on this site Intel Itanium 64 Bit processor Intel 80386 Reference Programmer's Manual Our Partners: |
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prev: 10.1 Processor State After Reset next: 10.3 Switching to Protected Mode
10.2 Software Initialization for Real-Address ModeIn real-address mode a few structures must be initialized before a program can take advantage of all the features available in this mode.
10.2.1 StackNo instructions that use the stack can be used until the stack-segment register (SS) has been loaded. SS must point to an area in RAM.
10.2.2 Interrupt TableThe initial state of the 80386 leaves interrupts disabled; however, the processor will still attempt to access the interrupt table if an exception or nonmaskable interrupt (NMI) occurs. Initialization software should take one of the following actions:
10.2.3 First InstructionsAfter RESET, address lines A{31-20} are automatically asserted for instruction fetches. This fact, together with the initial values of CS:IP, causes instruction execution to begin at physical address FFFFFFF0H. Near (intrasegment) forms of control transfer instructions may be used to pass control to other addresses in the upper 64K bytes of the address space. The first far (intersegment) JMP or CALL instruction causes A{31-20} to drop low, and the 80386 continues executing instructions in the lower one megabyte of physical memory. This automatic assertion of address lines A{31-20} allows systems designers to use a ROM at the high end of the address space to initialize the system.
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Chapter 10 -- Initialization |